1. Field of the Invention
The subject invention relates to optical systems and, more particularly, to an improved infrared semiconductor optical filter epitaxially joinable with an infrared detector.
2. Description of Related Art
State-of-the-art long wavelength infrared (LWIR) optical filters use multilayer dielectric (MLD) interference to transmit the pass band and reflect the out-of-band energy. To achieve high out-of-band rejection (low transmission T.ltoreq.10.sup.-4) over broad wavelength regions, state-of-the-art MLD interference filters employ many layers, for example, up to 300. These layers are deposited at high temperatures, resulting in a very thick, highly stressed coating. Since the coating has such high stress, it must be deposited on two or more substrates, or the layers will not adhere.
Such filters are thus relatively complex. They are also very expensive. A filter one inch in diameter with high out-of-band rejection presently costs about $100,000.00. Accordingly, it has appeared desirable to the inventor to develop an alternate approach to achieving optical band-pass filtering, which is more economical, less complex, and not subject to the stress problems of the prior art.